Laminated glass is utilized in a broad spectrum of products including safety glass found in automobile windshields, windows in trains, airplanes, ships, and can be found in some form in virtually all transportation machinery. Safety glass is characterized by high impact and penetration resistance and does not scatter glass shards and debris when shattered.
Laminated glass typically consists of a sandwich of two glass sheets or panels bonded together with an interlayer of a polymeric film or sheet, which is placed between the two glass sheets. One or both of the glass sheets may be replaced with optically clear rigid polymeric sheets, such as sheets of polycarbonate materials. Laminated articles have further evolved to include multiple layers of glass and polymeric sheets bonded together with interlayers of polymeric films or sheets.
The interlayer utilized, is typically a relatively thick polymer sheet which is well known for it's durability, as well as its to bond effectively to glass, thus creating a far safer product in the event of a crack or crash. In general, it is desirable that these polymeric interlayers possess a combination of characteristics including very high optical clarity, low haze, high impact resistance, high penetration resistance, excellent ultraviolet light resistance, good long term thermal stability, excellent adhesion to glass and other rigid polymeric sheets, low ultraviolet light transmittance, low moisture absorption, high moisture resistance, and excellent long term weatherability, among other requirements.
Laminated articles are most commonly formed by subjecting the assembly to elevated temperatures and pressures in an autoclave to bond the components.
Non-autoclave processes are generally considered to be less robust, and have a greater yield loss associated with adhesion and lamination failures in the finished article. Fabricators exercise greater care at process control parameters to achieve the desired adhesion levels and clarity for the finished article. Trapped voids of air and moisture between the layers of the laminate are most often to blame for the defects in the finished laminate. However, even with the most stringent attention to details, lamination integrity failures and cosmetic defects (edge bubbles) may still occur with regularity and without sufficient understanding of the cause. Many different attempts have been made to improve the reliability of the non-autoclave processes utilized in producing these laminates, but heretofore, none have proven satisfactory. See, e.g., U.S. Pat. Nos. 3,234,062, 3,852,136, 4,341,576, 438,595, 4,398,979, and 5,536,347 and EP patent 1235683B1. See also U.S. Pat. No. 6,342,116 (a multi-stage process for laminating multi-layer pre-forms into laminated glazing assemblies where the pre-forms are heated to an assembly or bonding temperature in a heating chamber, while still being subjected to vacuum).